Aircraft are generally provided with landing gear comprising a plurality of undercarriages, including a nose undercarriage and main undercarriages, the main undercarriages being fitted with brakes. Various actuators are associated with these undercarriages, including the following;                braking actuators mounted on the undercarriage in association with the wheels for braking the aircraft.The brakes are generally hydraulic brakes or electromechanical brakes;        steering actuators for steering the steerable wheels carried by the various undercarriages making up the landing gear, e.g. by the nose undercarriage, or indeed on certain aircraft, by the main undercarriages; and        drive actuators for retracting or extending undercarriages and the associated doors or hatches.These actuators comprise both drive cylinders and locking catches for holding the undercarriages or the hatches in the closed position.        
In order to power the various actuators, i.e. feed energy to them, use is generally made of the main power supply of the aircraft, as associated with the engines of the aircraft. The main power supply may comprise hydraulic pumps or electricity generators that are driven directly by the engines of the aircraft. The hydraulic pumps may also be driven by electric motors, themselves powered by the electricity generators of the aircraft.
Document CA 2 479 482 discloses an aircraft fitted with various hydraulic power supplies: a main power supply comprising pumps driven by electric motors and situated in the vicinity respectively of each of two main undercarriage and of the nose undercarriage, and a local power supply comprising two pumps driven by the wheels of the nose undercarriages when the aircraft is running on the ground. The local power supply is used in an emergency, in the event of the main power supply failing.